ISO 11904-1:2002

Overview

ISO 11904-1:2002 - "Acoustics - Determination of sound immission from sound sources placed close to the ear - Part 1: Technique using a microphone in a real ear (MIRE technique)" - defines a standardized method for measuring sound exposure when the source is close to the ear. The standard uses miniature/probe microphones inserted in human ear canals (the MIRE technique) to measure ear-canal sound pressure, then converts those readings into corresponding free-field or diffuse-field related equivalent continuous A‑weighted sound pressure levels. Applicable frequency range: 20 Hz to 16 000 Hz.

Key topics and technical requirements

• Measurement principle: direct ear-canal measurement with probe microphones and conversion to free-field or diffuse-field levels so results can be compared with established exposure criteria.
• Instrumentation: specifications and checks for ear-canal microphones, reference field microphones, filters and calibration procedures.
• Subjects and safety: selection of human subjects, ear-canal measurement positions, safe mounting of probes and positioning considerations.
• Conversion & weighting: methods to convert measured ear-canal sound pressure to free-field or diffuse-field related sound pressure levels; application of A-weighting and summation to produce equivalent continuous A-weighted levels (Leq, A).
• Frequency responses: procedures for determining human free-field and diffuse-field frequency responses and deriving banded corrections.
• Uncertainty and reporting: requirements for test reporting and informative annexes (Annex A and B) giving examples of measurement uncertainty analysis.

Applications and who uses it

ISO 11904-1 is used where conventional field measurements (with the person absent) do not accurately represent ear exposure because the source is near the ear. Typical use cases:

• Testing and certification of headphones, earphones and in-ear devices
• Assessment of hearing protectors with communication systems
• Workplace noise exposure evaluations for close-to-ear sources (e.g., portable audio equipment, certain tools)
• Product development and verification for consumer audio and professional communication headsets
• Occupational hygienists, acoustic laboratories, manufacturers, and regulatory bodies performing noise compliance, hearing conservation, and safety testing

Practical value

• Produces representative, human-based measures of ear exposure using the MIRE technique, enabling accurate assessments against occupational noise limits and design requirements.
• Converts ear-canal data to commonly used reference levels (free-field/diffuse-field) for compatibility with other standards and regulations.

Related standards

• ISO 11904-2 (manikin technique)
• ISO 8253-2, IEC 60268-7, IEC 60942 and related IEC/ISO documents referenced for instrumentation, calibration and audiometric practices.

Keywords: ISO 11904-1:2002, MIRE technique, microphone-in-real-ear, acoustics standard, sound immission, ear canal measurements, free-field related A-weighted, diffuse-field, workplace noise assessment, headphones testing.